1. Field of the Invention
The present invention relates to a semiconductor component, in particular a field-effect-controllable transistor.
DE 198 28 191 C1 discloses a lateral high-voltage transistor having, on an n-conducting substrate, an epitaxial layer in which source and drain zones and also a channel zone surrounding the source zone are formed. Trenches are provided in the epitaxial layer. The sidewalls of these trenches are heavily doped with a complementary dopant with respect to the rest of the epitaxial layer. A conductive channel in the channel zone can be controlled by means of a gate electrode insulated from the channel zone.
When a source-drain voltage is applied, a space charge zone propagates in this transistorxe2x80x94if no gate-source voltage is appliedxe2x80x94proceeding from the source zone, and as the voltage rises, the space charge zone gradually reaches the complementarily doped sidewalls of the trenches in the direction of the drain zone. Where the space charge zone propagates, free charge carriers of the doped sidewalls of the trenches and free charge carriers of the surrounding epitaxial layer mutually compensate one another. In these regions in which the free charge carriers mutually compensate one another, a high breakdown voltage results for lack of free charge carriers. The reverse voltage of the transistor can be set by means of the doping of the trenches, the epitaxial layer preferably being highly doped, as a result of which the transistor has a low on resistance when the gate is driven.
Such transistors having a low on resistance but a high reverse voltage are currently available only as discrete components, that is to say only the transistor is realized in a semiconductor body. However, for many applications, for example for switching loads, it is desirable to integrate a transistor as a switching element and its associated drive circuit, for example using CMOS technology, in a single semiconductor body.
The semiconductor component according to the invention has a semiconductor body with a substrate of a first conduction type and, situated above the latter, a first layer of a second conduction type. In the layer of the second conduction type there is formed a channel zone of the first conduction type with a first terminal zone of the second conduction type arranged adjacent to it. Furthermore, a second terminal zone of the second conduction type is formed in the second layer. In a transistor, the first terminal zone forms the source zone and the second terminal zone forms the drain zone. The source zone is surrounded in the second layer by the channel zone, in which a conductive channel can form as a result of the application of a drive potential to a control electrode or gate electrode which is arranged in a manner insulated from the channel zone.
In order that the first layer can be highly doped for the purpose of achieving a low on resistance, and, on the other hand, in order that a high reverse voltage is achieved, compensation zones of the first conduction type are provided in the first layer, a second layer of the second conduction type being formed between these compensation zones and the substrate of the first conduction type, said second layer preferably being doped more lightly than the first layer.
In integrated circuits, the substrate is usually at a reference-ground potential. The second layer then prevents charge carriers from passing into the substrate when a high potential is applied to one of the terminal zones; in the substrate said charge carriers could pass to other circuit components in the semiconductor body, for example to a drive circuit, and interfere with their functioning. In the event of a large potential difference between one of the terminal zones and the substrate, the second layer is depleted on account of the space charge zone which then forms, that is to say the free charge carriers in the second layer and free charge carriers of the substrate and/of the compensation zones mutually compensate one another. The second layer then forms a potential barrier for free charge carriers of the first conduction type between the first layer and the substrate.
One embodiment of the invention provides a boundary zone which extends in the vertical direction of the semiconductor body. This boundary zone preferably reaches in the lower region of the semiconductor body as far as the substrate and extends in the upper region of the semiconductor body as far as the channel zone or is arranged offset with respect to the channel zone in the lateral direction of the semiconductor body and reaches as far as a first surface of the semiconductor body. The boundary zone of the first conduction type, which is thus doped complementarily with respect to the first layer, bounds the semiconductor component according to the invention in the lateral direction of the semiconductor body. A charge carrier exchange in the lateral direction is prevented by the boundary zone, as a result of which further semiconductor circuits, for example drive circuits using CMOS technology, can be realized beyond said boundary zone, the drive circuit and the semiconductor component according to the invention not mutually interfering with one another.
One embodiment of the invention provides for the compensation zones in the first layer to extend in a pillar-shaped manner in the vertical direction of the semiconductor body, in which case, according to a further embodiment, at least some of the compensation zones adjoin the channel zone. In transistors, the source zone as first terminal zone and the channel zone are usually short-circuited, so that the compensation zones adjoining the channel zone are at the same potential as the first terminal zone.
According to a further embodiment of the invention, the compensation zones are of spherical design and arranged such that they are distributed in the first layer of the second conduction type.
A further embodiment provides for the first layer of the second conduction type to be weakly doped and for more heavily doped second compensation zones of the second conduction type to be formed adjacent to the compensation zones, which, in particular, are of pillar-shaped design. When a high voltage is applied between the first and second terminal zones, the compensation zones of the first conduction type and the respectively adjacent second compensation zones of the second conduction type mutually deplete one another, that is to say the free charge carriers of the compensation zone of the first conduction type and the free charge carriers of the second compensation zone of the second conduction type mutually compensate one another.
One embodiment of the semiconductor component according to the invention provides for the second terminal zone to be formed in a well-like manner in the region of the first surface of the semiconductor body or the first layer. In this exemplary embodiment, the charge carriers move between the first and second terminal zones essentially in the lateral direction of the semiconductor body. A further embodiment provides for the second terminal zone to extend in the vertical direction of the semiconductor body as far as the second layer and to run in the region of the second layer in the lateral direction of the semiconductor body below the first terminal zone. In this embodiment, in which the lateral section of the highly doped second terminal zone runs in a manner buried in the semiconductor body and can be contact-connected by means of the vertical section at the first surface of the semiconductor body, the charge carriers move essentially in the vertical direction of the semiconductor body.
A further embodiment provides for vertical sections of the second terminal zone and the laterally running section of the second terminal zone to enclose the first terminal zones and at least some of the compensation zones in a well-like manner.
In accordance with an added feature of the invention, the first layer has a number of dopant atoms of the first conduction type and a number of dopant atoms of the second conduction type that are approximately identical.